This invention relates to a method for making organic cation tetrakis(Faryl)borate salts from an alkali metal tetrakis(Faryl)borate. When the organic cation is a protic ammonium cation or a triarylmethyl cation, the tetrakis(Faryl)borate salt is useful as a cocatalyst for metallocene-catalyzed polymerization. When the organic cation is an onium cation, the tetrakis(Faryl)borate salt is useful as an initiator in the crosslinking of polyorganosiloxanes.
It has been found that, when dry, alkali metal tetrakis(Faryl)borates are thermally sensitive. Alkali metal tetrakis(Faryl)borates are also sensitive to shock. These sensitivities clearly indicate potential hazards in the handling and processing of such compounds. Because alkali metal tetrakis(Faryl)borates are useful intermediates in the preparation of organic cation tetrakis(Faryl)borates, it would be very desirable to minimize or eliminate these sensitivity problems.
Surprisingly, it has been discovered that the presence of solvent, especially a halogenated hydrocarbon, mitigates both the thermal and shock sensitivity of alkali metal tetrakis(Faryl)borates. Additionally, it has been found that the reaction time when forming triarylmethyl tetrakis(Faryl)borates from alkali metal tetrakis(Faryl)borates is significantly reduced when operating in halogenated hydrocarbons. In particular, the reaction of 20 grams of potassium tetrakis(pentafluorophenyl)borate with triphenylmethyl chloride is complete in under twenty minutes in dichloromethane, as compared to over ten hours for the same reaction on the same scale in hexane.
An embodiment of this invention is a process for producing protic ammonium tetrakis(Faryl)borate, an onium tetrakis(Faryl)borate, or a triarylmethyl tetrakis(Faryl)borate from a solution or slurry of an alkali metal tetrakis(Faryl)borate in a liquid ethereal medium or liquid hydrocarbyl medium. This process comprises substituting the liquid ethereal medium or liquid hydrocarbyl medium with at least one halogenated hydrocarbon, without isolating the alkali metal tetrakis(Faryl)borate, to form a new slurry or solution. At least a portion of the new slurry or solution is mixed together with a salt selected from a) a protic ammonium salt, b) an onium salt, and c) a triarylmethyl salt, to produce a protic ammonium tetrakis(Faryl)borate, an onium tetrakis(Faryl)borate, or a triarylmethyl tetrakis(Faryl)borate. The triarylmethyl cation has three aryl groups bound to a central carbon atom. The protic ammonium cation has the formula [R3NH]⊕, in which each R is independently a hydrocarbyl group containing up to about thirty carbon atoms, and the onium cation has the formula [ERn]⊕, wherein E is an element of any of Groups 15-17 of the Periodic Table, wherein each R is independently a hydrocarbyl group containing up to about thirty carbon atoms, and wherein n is equal to the valence of E plus one. For labeling of the groups of the Periodic Table, see for example, the Periodic Table appearing in Chemical and Engineering News, Feb. 4, 1985, 69, 26.
The borate anion has four fluorine-containing aryl groups, each of which has bonded directly to an aromatic ring at least two fluorine atoms, or at least two perfluoro hydrocarbyl groups, or at least one fluorine atom and at least one perfluorohydrocarbyl group. It is preferred that at least two fluorine atoms, or at least two perfluorohydrocarbyl groups are bonded directly to an aromatic ring. Each position on the aromatic ring(s) of the Faryl group that is not a fluorine atom or a perfluorohydrocarbyl group is substituted by a hydrogen atom, a hydrocarbyl group, an alkoxy group, or a silyl group. The Faryl groups may be the same or different from each other; it is preferred that all four Faryl groups are the same.
Further embodiments of this invention will be apparent from the ensuing description and appended claims.